ARM: Remove unused flag in lithium-codegen.

This flag was added by commit r13585.

BUG=

Review URL: https://codereview.chromium.org/12258013

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13677 ce2b1a6d-e550-0410-aec6-3dcde31c8c00